1. Field of the Invention
The present invention relates generally to the construction and use of intravascular catheters. More particularly, the invention relates to atherectomy catheters having means at their distal ends for severing stenotic material.
Human vascular systems commonly become constricted, or stenotic, due to the accumulation of atheromatous material on the inner walls of the vascular lumens. When blood vessels such as arteries or vein grafts are involved, this condition is known as arteriosclerosis, or atherosclerosis. Atherosclerosis occurs naturally as a part of the aging process, but may also be aggravated by such factors as diet, hypertension and heredity. The intravascular deposits, or atheromas, tend to restrict blood flow causing ischemia, and in acute cases can result in myocardial infarction. The material properties of the deposits vary widely, with some deposits being relatively soft and others fibrous or calcified.
Many approaches for removing such deposits have been proposed. Generally, the approaches for removing atheromas have employed cutting, grinding or thermal ablation techniques. Of particular interest to the present invention are atherectomy devices and methods which employ a means for severing atheromatous material from the vessel wall.
In a typical atherectomy operation, a catheter having a suitable diameter is introduced into a lumen of the patient's vascular system and positioned adjacent the target material. A cutter blade provided at the distal end of the catheter is brought into contact with the target material. The catheter may either be a front-end cutting type or a side-cutting type. Front-end cutting atherectomy catheters are particularly useful in penetrating non-crossable lesions as they can "drill" through the lesion. Side-cutting atherectomy catheters are particularly useful in "debulking" a stenosed region and may employ an inflatable balloon disposed opposite the cutter blade to assist the blade in removing successive layers of stenotic material.
Although atherectomy catheters have enjoyed substantial success in treating vascular stenoses, some designs suffer from certain limitations. In particular, severing or abrading of the occluding material can result in the release of atheromatous particles which may then embolize the vasculature. Such emboli will lodge in the narrower regions of the vascular system and may significantly restrict the blood flow in critical regions of the vascular system, such as the coronary arteries. This may, in turn, endanger the patient's health.
Front-end cutting catheters are particularly prone to the release of large emboli into the vascular system. Some front-end cutting devices employ an exposed blade that severs or abrades the stenotic material. Usually provisions are made for aspirating the removed material, together with a substantial volume of blood, back through the catheter so that it is not released in vascular system. See, for example, U.S. Pat. Nos. 4,857,046, and 4,772,258. The use of aspiration with a rapidly rotating blade, however, cannot be relied on to capture all of the atheromatous material which is liberated during the atherectomy procedure.
Side-cutting catheters generally reduce the propensity for release of emboli into the vascular system since a housing is used to contain the blade and the housing is pressed firmly against the vessel wall having the atheromatous material. Most particles severed from the wall collect within the housing; more so than with front-end cutting catheters. See, for example, U.S. Pat. No. 4,669,469 and EPO Publication No. 0 163 502.
For these reasons, it is desired to provide atherectomy catheters that can remove stenotic material in a more controlled fashion with a minimum risk of releasing emboli into the vascular system. In particular, it is desired to invaginate atheromatous material within a substantially enclosed structure as the material is severed from the stenosed portion of the vascular lumen. Additionally, it is desired to provide a means for withdrawing the captured material from the enclosed structure. Also, it is desirable to provide methods for severing occluding material in such a manner as to ensure that it is retained within the means for containment until the catheter can be withdrawn from the patient. Finally, it would be desirable to provide atherectomy catheters which combine the ability of front-end cutters to penetrate lesions with the ability of side cutters to debulk stenosed regions.
2. Description of the Background Art
U.S. Pat. Nos. 4,857,046; 4,772,258; 4,745,919; and 4,653,496, all describe front-end cutting atherectomy catheters and the disclosure of each is incorporated herein by reference. Several of these patents further disclose use of a helical cutting blade to sever material from the vascular lumen. U.S. Pat. Nos. 4,685,458; 4,669,469; 4,627,436; and EPO Publication No. 0 163 502 each describe a side-cutting atherectomy catheter and the disclosure of each is incorporated herein by reference. These side-cutting devices may employ an inflatable balloon opposite an opening in the housing that contains the cutting blade. U.S. Pat. No. 4,020,847, describes a biopsy catheter having a slotted cylinder at its distal end, where the slot includes a cutting edge for severing tissue as the catheter is rotated.